1. Field
This document relates to a touch sensing device with touch sensors embedded within a pixel array and a driving method thereof.
2. Related Art
A user interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices as they desire. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technologies have continuously evolved to increase user's sensibility and handling convenience. The user interface has been recently developed to touch UI, voice recognition UI, three-dimensional (3D) UI, etc.
The touch UI has been installed in portable information devices such as smartphones, and widely applied to laptop computers, computer monitors, home appliances, etc. The technology of embedding touch sensors into a pixel array of a display panel (hereinafter, “in-cell touch sensor technology”) has been recently proposed. The in-cell touch sensor technology allows for installing touch sensors in the display panel without increasing the thickness of the display panel. The touch sensors are connected to pixels through parasitic capacitance. In a driving method thereof, a period for driving pixels (hereinafter, “display driving period”) and a period for driving touch sensors (hereinafter, “touch sensor driving period”) are time-divided in order to reduce mutual effects caused by the coupling between the pixels and the touch sensors.
The in-cell touch sensor technology uses an electrode connected to the pixels of the display panel as electrodes for the touch sensors. For example, the in-cell touch sensor technology may use the method of dividing a common electrode into sections to supply a common voltage to the pixels of a liquid crystal display device and using the sections of the common electrodes as electrodes for the touch sensors. The same common voltage should be applied to all of the pixels; however, the common voltage becomes non-uniform on a large screen when the common electrode is divided into sections for the touch sensors, which may lead to picture quality degradation.
Referring to FIGS. 1 to 3, a common electrode COM is divided into a plurality of sensors C1 to C4 using the in-cell touch sensor technology. Sensor lines L1 to L4 are connected to the sensors C1 to C4, respectively.
During the display driving period Td, the common voltage Vcom for pixels is supplied to the sensors C1 to C4 through the sensor lines L1 to L4. During the touch sensor driving period Tt, a sensor driving signal Tdrv is supplied to the sensors C1 to C4 through the sensor lines L1 to L4.
The length of the sensor lines L1 to L4 differs depending on the positions of touch sensors. The differences in length between the sensors lines L1 to L4 cause variations in the delay time of the common voltage Vcom applied to the sensor C1 to C4 with the touch sensor positions, resulting in non-uniform picture quality.
For example, as shown in FIG. 3, the delay time of the common voltage Vcom applied to the first sensor C1 through the first sensor line L1 is longer than the delay time of the common voltage Vcom applied to the fourth sensor C4 through the fourth sensor line L4. This is because the first sensor line L1 is longer than the fourth sensor line L4, leading to longer resistor-capacitor RC delay. Accordingly, the first sensor C1 has a lower voltage than the fourth sensor C4 even if the same voltage is applied to the first and fourth sensor lines L1 and L4. Due to the RC delay, the delay time of the sensor driving signal Tdrv also varies depending on the touch sensor positions.
On a large screen display device, the differences in length between the sensor lines L1 to L4 are large. Therefore, the conventional in-cell touch sensor technology makes non-uniform the common voltage Vcom applied through the sensor C1 to C4 during the display driving period Td on a large screen display device, causing degradation in the display device's picture quality.
A large-screen display device has larger parasitic capacitance than a smaller display device due to the coupling between in-cell touch sensors and pixels. If the size and resolution of a touch screen increases, the parasitic capacitance increases. This results in a reduction in touch sensitivity and touch recognition accuracy. Therefore, there arises the need to apply the in-cell touch sensor technology to the touch screen of a large-screen display device to minimize the parasitic capacitance of the touch sensors.